Amplifying system



Inventor: william @whs-Lg,

His Attorney.

Patented Dec. l9, 1924.

UNITED STATES FIC E PATENT oF WILLIAM C. WHITE, F SCHENECTADY, NEW YORK, ASSIGNOB TO GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK. I

AMPLIFYING SYSTEM.

Application led July 8,

ing systems and particularly to Systems in which a plurality of amplifiers are connected in parallel.

The object of my invention is to preventin such ar system the generation of oscillations. A more specific object of my invention is to prevent the generation of oscillations in an amplifying system in which electron discharge ampllfiers are connected in parallel.

In the employment of electron discharge amplifiers having the usual grid or input circuit and plate or output circuit, it has been found that there is a marked tendency toward the production of oscillations by reason ofthe natural coupling which exists between the input and output circuits. When it is desired to employ a plurality of these amplifiers in parallel this tendency is magnified because of the fact that the capacity coupling which exists betweenthe circuits inside of the tubes and the capacity and magnetic coupling of the circuits outside the tubes becomes much greater than when a single amplifier is employed. I have discovered that 3 5 this tendency may be entirely eliminated by including in the grid or input circuit of only one of the amplifiers a small inductance.

The novel features which I believe to be characteristic of my invention are Set forth 0 in particularity in the appended claims, the

invention itself, however, as to both its organization and methodv of operation will best be understood by reference to the following description taken in connection with the accompanying drawing in which I have indicated diagrammatically one circuit organization w ereby my invention may be carried into effect.

The system indicated in the drawing comprises a plurality of electron discharge amplifiers, 1, 2,' 3, to 7, each having the usual cathode 8, grid 9, and plate or anode 10.- A source of current 11 supplies current to all of the cathodes in parallel for heating them to incandescence to cause them 1919. Serial No. 309,306.

to emit electrons. The grid vor input circuits of all of these amplifiers which include the cathodes 8 and grids 9 are connected in parallel and a common portion of these grid circuits includes the secondary 12 of a transformer by means of which the currents to be amplified are supplied to the system. In the present case I have indicated 'as the source of the currents to be amplified a telephone transmitter 13 which is in the local circuit comprising the primary 14 of the transformer and the battery 15. My invention is equally well adapted, however, for use in amplifying systems for radio frequency currents. The plate or output circuits of the amplifiers which include the cathodes 8 and anodes 10 are also connected in parallel and are all supplied with current from a source 16. The common part of the plate circuits also includes the primary -17 of a transformer 18, thesecondary of which supplies amplified currents to any circuit desired and which may be connected to the conductors 19. There is resent in the ampliiers of the type here involved a certain amount of capacity between the different electrodes. This capacity serves as a coupling between the grid and plate circuits,

while the capacity between the elements of a single device is ordinarily small, where fa plurality of devices are employed as in the present arrangement the capacity coupling between the circuits becomes appreciable.

'There is also present in the circuits a cer-- tain amount of inductance. due to the leads and this combination produces a tendency inthe system to the generation of oscillations the frequency of which will be determined by the capacity and inductance of the system. These oscillations will ordinarily be of' comparatively high frequency and this tendency is very troublesome. In some cases when the system starts to oscillate the ampliliers will no longer operate, fuses inserted at various places for the protection of the system will be blown, and the source of supply current may be broken down. I have found that this tendency for the production of oscillations may in some cases be entirely eliminated by the insertion of an inductance 20 in the grid circuit of one of the amplifiers. This inductance' may be comparatively small, afew microhenries being suiiicient for 'the purpose. It is important for the suppression 0f oscillations that this Vinductance be placed in that portion of the grid circuit of the amplifier to which it is connected which is close to grid of that particular amplifier, that is the beneficial results Will not be obtained when the inductan'ce is placed in the circuit in such a way that it is common to all of 'the grid circuits. The reason Why the use of this inductance produces the results sets forth is not entirely clear. It seems probable. however, that its effect is to shift the phase of the current thron'rh the coupling capacity so that it is no onger in the proper phase to cause the generation of oscillations. In the present case I have shown a single group of amplifiers and have -assumed that these amplifiers are located comparatively close together. In case several groups of amplifiers are used or the amplifiers are located so far apart that the leads joining them are of considerable lengths, the inductance of the leads may become so large that it will be found desirable to employ inductance in the grid circuits of more than one amplifier.

While I have indicated and described only i one system for carrying my invention into effect, it Will be apparent to one skilled in the art that my invention is by no'means limited to the particular organization shown and described but that many modifications in the circuit arrangements used as well as in the apparatus employed may, be made Without departing from the scope of my invention as set forth in the appended claims.

What I claim as new and desire to secure by Letters Patent of the vUnited States, is

l. The combination in an amplifyin system of a plurality of electron disc arge amplifiers connected in parallel and having plate and grid circuits, means for supplying currents to be amplified to the grid circuits of-said amplifiers, means for supplying plified current from the plate circuits of the amplifiers, and an inductance of small value connected in the grid circuit of one of said amplifiers for preventing the. generation of ligh frequency oscillations hy said ampliers.

3. The combination in an amplifying system of a plurality' of electron discharge a-mplifiers connected in parallel and having plate and grid circuits, means for supplying audio frequency currents to be amplified to the grid circuits of said amplifiers, means for supplying amplified audio frequency currents from the plate circuits of said amplifiers, and means connected in the grid circuit of only one of said amplifiers for preventing the generation of high frequency oscillations by said amplifiers.,

4. The combination in an amplifyin system of a plurality of electron disc arge amplifiers connected in parallel and having plate and grid circuits, means for supplying currents to be amplified to the grid circuits of said amplifiers, means for'supplying amplified currents from the plate circuits of said amplifiers, and an inductance of small value so connected to the system that the current in the grid circuit of only one of the amplifiers will flow through said inductance.

5. The combination in an amplifying system of a plurality of amplifiers having 1nput circuits connected in arallel and output circuits connected in para lel, means for supplying currents to be amplified to said input circuits, means for supplying amplified currents from saidoutput circuits and means connected in the input circuit of only one of said amplifiers for preventing the generation of oscillations-in the system.

6. The combination of an electron discharge device having plate and grid circuits containing inductances and means for preventing the production of undesired oscillations in said circuits, comprising an inductance of small value in comparison with the other inductances of the circuits connected in the grid circuit close to the grid.

7. The combination of a plurality of electron discharge devices having plate and grid circuits portions of which are common to all of said devices, and means for preventing the production-of undesired oscillations in said circuits, comprising an inductance--of small value connected in a portion, ofthe grid circuit of one of said devices which is individual to that device. p

8. In a system comprisingaffnumber of discharge devices having plate, gridy and filamentv electrodes, corresponding electrode circuits therefor in parallel, and a choking inductance in one of said corresponding electrode circuits.

In witness whereof, I havehereunto set my hand this 7th day of July, 1919.

v-WILLIAM C. WHITE. 

